Fatty Acid Synthase (FASN) is an enzyme that catalyzes the de novo synthesis of long-chain fatty acids from acetyl-CoA and malonyl-CoA in cells. Normal cells (except liver and adipose tissue) have low levels of FASN activity. In rapidly proliferating cancer cells fatty acids can be synthesized de novo to provide lipids for membrane formation. Our general hypothesis is that FASN is a promising therapeutic target for invasive breast carcinomas. FASN is highly expressed in invasive breast and other carcinomas, and is prominent in higher grade tumors correlating with poor prognosis. Our data shows that 60% of invasive breast carcinomas express high levels of FASN and FASN expression is a marker for poor prognosis and poor disease free survival. Interestingly, FASN is highly coexpressed with the three breast cancer histopathological groups: Estrogen Receptor positive (ER+), HER2 3+ overexpressing (HER2+) and triple negative (TN) [which do not express ER, Progesterone Receptor (PgR), and HER2+). Our preliminary studies show that pharmacological inhibition of FASN in breast cancer synergizes with chemotherapeutical agents such as Taxol, and with antiestrogens and trastuzumab targeted therapies increasing growth inhibition and apoptotic cell death in vitro and in vivo. We demonstrated that blockage of FASN inhibits tumor growth and induces apoptosis, triggering deteriorating effects which lead to apoptotic cell death including: i inhibition of palmitate, hence the inhibition of sphingolipids synthesis; ii) mitochondria damage and release of Cyt c; iii) increase Reactive Oxygen Species (ROS) generation; and iv) upregulation of BH3-only family proteins (Noxa, Bim, Puma). In this proposal we will extend these concepts using a variety of biochemical, genetic and therapeutic approaches: First, we will examine the clinical value of FASN as a theranostic (predictive) marker for response to targeted therapy in breast-cancer patients, in adjuvant and neoadjuvant setting. Second, we will assess the role of: i) BH3-only proteins Noxa, Bim and Puma in FASN inhibition induced apoptosis: ii) the synergistic effect of inhibitors of FASN and Taxol induced apoptosis; iii) the lnk between FASN inhibition and increased ROS production and BH3-only protein upregulation. Last, we will perform preclinical studies to assess a newly develop anti-FASN agent in combination with antiestrogens, Trastuzumab and Taxol. This proposal will provide new insight into the action of FASN inhibitors and the information needed to translate our findings into the clinic. Our goal is to develop novel rationally designed therapeutic approaches for breast cancer.